Method of forming a solar collector having multiple composite plies

ABSTRACT

A solar collector for use in concentrating solar rays into a high flux density image is formed from laminate plies. Electricity is produced by superimposing the image onto a concentrated photovoltaic cell. Plies are cut from a composite sheet that is made up of carbon fibers in a thermoset polymer, where the carbon fibers run generally parallel with one another. By varying how the plies are cut from the sheet, carbon fibers in different plies are oriented at alternating angles in the plies. The plies arc stacked to form a laminate, where the carbon fibers in each ply are at an angle with carbon fibers in adjacent plies. The plies may include alignment tabs to control the angle between adjacent plies. Pressing the laminate in a heated die and cooling the die with forced convection and then a fluid bath forms a shell for the solar collector.

BACKGROUND

1. Field of Invention

The invention relates generally to a solar collector. More specifically, the present invention relates to a method of forming a solar collector with a substrate formed from a laminate of plies of a composite,

2. Description of Prior Art

Solar collection systems that concentrate solar energy generally employ a number of collectors; each having a reflective side configured to focus the reflected light. Focusing the reflected light typically entails forming an image that is cast onto a solar conversion cell. Collector configurations must be distinct and carefully shaped to focus the concentrated solar energy onto a solar conversion cell. A misshaped collector usually forms an out of focus image with a less homogenous flux density than a focused image, thereby reducing system efficiency.

Many obstacles exist when working a material so the reflective, or optical, side of each collector is sufficiently precisely configured to generate a desired image. Manufacturing obstacles are especially prevalent when solar energy collectors are mass produced. For example, while the ram and die of a metal stamping process may be precisely configured to form a collector shell, the stamped shell may not have the desired configuration. Internal stresses in the material being stamped can bend the shell from a desired configuration; where the internal stresses may be inherent in the material or introduced during stamping. Also, ram and die sets can wear over time and eventually form collector shells with undesired configurations.

Solar collectors are typically made from a material with some stiffness so the collectors can retain their shape long term and be useable for many years. Moreover, solar collection and conversion systems often consolidate the collectors into a solar array to boost the electricity generating capacity of the conversion system. Thus the material for the collectors should be strong enough to resist deformation, such as from routine handling or from creep, but also be light enough for handling and mounting.

SUMMARY OF THE INVENTION

Provided herein is a method of forming a solar collector for use in concentrating solar rays into a high flux density image. Electricity is produced by superimposing the image onto a concentrated photovoltaic cell. Plies are cut from a composite sheet that is made up of carbon fibers in a thermoset polymer, where the carbon fibers run generally parallel with one another. By varying how the plies are cut from the sheet, carbon fibers in different plies are oriented at alternating angles in the plies. The plies are stacked to form a laminate, where the carbon fibers in each ply are at an angle with carbon fibers in adjacent plies. The plies may include alignment tabs to control the angle between adjacent plies. Pressing the laminate in a heated die and cooling the die with forced convection and then a fluid bath forms a shell for the solar collector.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an example embodiment of plies of composite that form a substrate in accordance with the present invention.

FIG. 2 is a perspective view of an example of the substrate of FIG. 1 formed into a collector shell in accordance with the present invention.

FIG. 3 is a side perspective view of an example of a collector formed from the collector shell of FIG. 2 in accordance with the present invention.

FIG. 4 is a perspective view of the stacking of cut plies of composite.

FIG. 5 is an exploded perspective view of the forming tools for the composite.

FIG. 6 is a side view of composite plies placed into the forming tools.

FIG. 7 is a side view of three forming tool sets placed between two heated press platens showing force and heat input.

FIG. 8 shows a side view of the forming tools taken out of the press and fan cooled.

FIG. 9 shows a side view of the forming tools being submerged in cooled water after fan cool.

FIG. 10 shows a perspective view of the final cured composite mirror shell.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout.

It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

FIG. 1 shows in a side perspective view a roll of tape 20 being unrolled so a portion of the tape 20 is laid out onto a cutting surface 21. The tape 20 is a composition that includes a thermoset resin 22, such as epoxy, and elongated carbon fibers 24 provided within the resin 22. The fibers 24 all run generally parallel with one another and are oriented so that they extend generally along the length of the tape 20. When rolled out onto the cutting surface 21, the tape 20 assumes a generally planar configuration. Adjacent the cutting surface 21 is a cutting apparatus 26, that in one example, is a computer numerical control (CNC) machine. A gantry 28 is provided with the cutting apparatus 26, wherein the gantry 28 includes a frame 30 on which a movable cutter assembly 32 is supported. The cutter assembly 32 is shown disposed over the portion of the tape 20 on the cutting assembly 21 and includes a blade 34 depending downward and into selective cutting contact with the tape 20. An elongate arm 36 extends between parallel portions of the frame 30, wherein the arm 36 is slideable lengthwise along the frame 30. The cutter assembly 32 is also slideable and in a lateral direction along the arm 36 in between ‘the frame members 30. An optional controller 38 is illustrated for delivering commands to the cutting apparatus 26 so the cutter assembly 32 can cut selected and specific shapes from the tape 20.

As illustrated in FIG. 2, the cutter assembly 32 has been manipulated to cut a series of composite plies 40 ₁-40 ₄ from the tape 20. In the example of FIG. 2, the plies 40 ₁-40 ₄ are rectangularly-shaped and disposed at various orientations along the length of the tape 20. That is, in examples where the plies 40 ₁-40 ₄ having an elongate side, the carbon fibers 24 may be disposed at different angles with respect to the lengthwise direction of the plies 40 ₁₋ 40 ₄ cut at different orientations.

Referring now to FIG. 3, illustrated in an overhead view are example plies 40 ₁-40 _(n). In this example, orientations of the carbon fibers 24 are shown to be at an angle with an axis A_(xn), of each of the plies 40 ₁-40 _(n). Also illustrated are tabs 41 that extend laterally outward from edges of each of the plies 40 ₁-40. Bores 42 are shown formed through each of the tabs 41. The tabs 41 may be useful for aligning the plies 40 ₁-40, when the plies are stacked on one another for forming a laminate. More specifically, and as shown in FIG. 4, the plies 40 ₁-40 _(n) are arranged so that alignment rods 43 intersect the bores 42 in each of the plies 40 ₁-40 _(n) thereby providing a precise stacking orientation of a series of successive plies 40 ₁-40 _(n).

Referring now to FIG. 5, an example of a die set 44 is shown in an end perspective view, wherein the die set 44 includes a lower convex portion 45. The convex portion 45 is a substantially solid rectangular piece and adapted to have a convex upper surface. The die set 44 includes a concave portion 46 that is shown disposed above the convex portion 45. The concave portion 46 has a downward facing concave shaped surface that corresponds to the convex shape of the convex portion 45. Elongate side rails 48 are shown adjacent the lateral sides of the convex and concave portions 45, 46, The side rails 48 may be attached to the convex portion 45 by threaded fasteners 50 that fit into bores 51 in the side rails 48 and convex portion 45.

Referring now to FIG. 6, the die set 44 is shown being used for shaping the stacked plies 40 ₁-40 _(n) into a laminate 52. Moreover, the side rails 44 are shown having grooves 54 that extends substantially the length of the side rails 44. The grooves 54 are on surfaces of the side rails 44 facing the lateral sides of the convex portion 45 and have a lower terminal end just above the upper lateral edges of the convex portion 45. The grooves 54 provide a space so the lateral edges of the plies 40 ₁-40 _(n) can expand when pressed between the concave and convex portions 45, 46 of the die set 44.

In the example of FIG. 7, multiple die sets 44, each having a laminate 52 disposed therein, are shown set between upper and lower platens 56, 58. In this example, a force F₁ is applied to the upper platen 56 while the lower platen 58 is supported to urge together the convex and concave portions 45, 46 and thereby apply a compressive force onto the laminate 52. In one example of use, the force F₁ is applied for the step of debulking the laminate 52 and removing any voids that may exist within the plies 40 ₁-40 _(n) (FIG. 6). Example pressures in the plies 40 ₁-40 _(n), for debulking can be in the range of about 200 psi to about 250 psi. In an optional embodiment of the example of FIG. 7, the platens 56, 58 are heated so that during the pressing process heat Q from the platens 56, 58 transfers to the die sets 44 and makes its way into the laminate 52 for curing the epoxy 22 therein. In one example embodiment, during the step of heating the laminate 52, the pressure within the laminate 52 is maintained at about 70 psi.

After the resin and the composite has cured, the die sets 44 are shown in FIG. 8 having been removed from between the platens 56, 58 and positioned into a stream of forced convection fluid flow 60. In this example, a rotating fan 62 generates a flow of air that is directed over the die sets 44 for cooling the die sets 44 and the shaped laminate 52 therein. As shown in FIG. 9, after a period of time of forced convection cooling, the die sets 44 can be placed within a container 60 having a cooling liquid 66, In one example, the cooling liquid 66 is room temperature water. It has been found that by cooling the heated laminate 52 as described above, the glass transition temperature of the resin within the laminate 52 can be crossed at a rate to eliminate or at least minimize forming internal stresses in the laminate 52. By controlling the cooling rate to avoid internal stress formation, a final product can be formed that does not deform when removed from the die set 44 and possesses sufficient strength to resist deformation and retain its shape over time.

In the example of FIG. 10, it can be seen that a convex side 68 and a concave side 70 are produced to then form a collector 72. Strategically shaping the convex and concave sides 45, 46 of the die set 44, a desired shape of the collector 72 can be achieved for forming a particular image on a concentrated photovoltaic cell. Moreover, a reflective material 74 may be applied onto the concave side 70 to allow for reflection of any solar rays that may be collected and reflected onto the photovoltaic cell.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. 

What is claimed is:
 1. A method of forming a solar collector comprising: providing a composite comprising substantially parallel elongated carbon fibers disposed in a thermosetting polymer; forming plies from the composite by cutting the composite into sections; stacking the plies into a laminate so that carbon fibers in each ply are oriented at an angle with carbon fibers in any adjacent ply; pressing the laminate into a shape having a concave side and a convex side; heating the laminate; and applying a reflective material to the concave side.
 2. The method of claim 1, wherein the angle between carbon fibers in any adjacent ply is selected from the group consisting of 0°, 30°, 45°, 60°, and
 900. 3. The method of claim 1, wherein the number of plies making up each laminate is selected from the group consisting of 6, 7, 8, 9, 10, 11, and
 12. 4. The method of claim 1, further comprising providing tabs on each ply for precisely arranging each ply in the laminate.
 5. The method of claim 1, wherein a portion of the step of pressing is a cold press for debulking the laminate that is at a pressure of about 200 psi to about 250 psi and wherein while heating the laminate the pressure is at about 70 psi.
 6. The method of claim 1, wherein the laminate is set in a die that is disposed in a platen assembly and wherein the pressure and the heat is applied by the platen assembly.
 7. The method of claim 6, further comprising removing the die from the platen assembly, cooling the die with a forced convection flow of fluid and then a fluid bath. 